Stereomicroscopes of the abovementioned type are known and are utilized for eye surgeries. In order for the vitreous body space inside of the eye to become visible, a dispersing lens (contact lens) is placed onto the cornea. A reflection-free illumination is achieved by separating the observation and the illumination beam path, by illuminating the vitreous body space by a cold-light conductor which is applied from the side to the eye. With the help of such stereomicroscopes and a surgery technique which has been developed within the last decade, it is possible by using the finest instruments to remove opacities in the eye (vitrectomy). The eye has the structure of a hollow sphere. Its interior, the socalled vitreous body space, is usually filled with a transparent, jellylike mass, the vitreous body. The cornea and the lens, which together with the iris (diaphragm) form the optical system of the eye, lie in front of the vitreous body. The objects which lie in front of the eye are reproduced onto the retina which lies behind the vitreous body through the optical system. If opaque foreign particles (for example blood) penetrate the vitreous body space, same becomes opaque, so that the incident rays can no longer reach the retina. In spite of a full functioning of the optical system and of the retina, such eyes are practically blind.
With the help of vitrectomy, it is possible to eliminate such injuries. Of course, the contact lenses which have been used up to now deliver a view of approximately 20.degree. (plano-concave contact lenses) up to a maximum of 35.degree. (biconcave contact lenses).
It is optically possible to extend the visual-field angle to up to 150.degree., which would make surgery substantially easier. Such a system of contact optics and spherical lens is known from the panorama funduscopy. Such a device is marketed by the Firm Rondenstock of Muenchen under the Trademark "Panfunduskop".
However, it is not possible to use this advantage in the vitrectomy, since the image in the surgery microscope appears inverted and left-and-right reversed. Thus manipulations in the eye are dangerously difficult and bimanually impossible.
An ophthalmoscope is known from U.S. Pat. No. 4,015,898, with which the background of the eye can be viewed. It is suggested in this patent to insert an Uppendahl prism for the inverting, reversing and separating of the beams, through which a stereoscopical, upright, unreversed image of the retina can be observed. However, the use of an Uppendahl prism assumes that an observing of the eye occurs in a straight, nonbent beam path, that is the eye of the observer must always lie rectinlinearly above the surface which is to be viewed. Whereas a bent beam path exists in a stereomicroscope, that is, the observer looks obliquely into the stereomicroscope, which is absolutely necessary for surgeries on the eye, because alone through this is assured an effortless working and operating, since otherwise the position of the surgeon would be unnatural and, which makes it more difficult yet, the distance from the eye of the surgeon to the object which is to be treated becomes too great.
The basic purpose of the invention is to construct a stereomicroscope with a bent beam path of the above-mentioned type such that the image which is obtained with the help of the panorama funduscopy appears upright and unreversed to the observer.
The beam path is parallel between the objective and the two prism telescopes, so that within certain limits the distance of said elements from one another can be changed without causing the beam path of the microscope to be significantly influenced with respect to the enlargement and the field of vision. The same is also true if, in addition, an enlargement changer is inserted between the collecting lens and the objective. It is possible through this to provide an optical element in said parallel beam path, which optical element places the image upright and unreversed and assures the bending of the beam path. It is not sufficient to carry out this upright positioning and unreversed positioning for each ocular separately, but to avoid a pseudostereoscopical effect, an exchange of the beam paths of the two microscope halves must also occur simultaneously. In order to obtain a turned, nonreflected image, the invention uses either a 90.degree.-reflection prism with a roof-surface pair or, however, a system which is formed of two mirrors which are arranged and fixed angularly to one another. The beam path which comes from the objective is fed to said system and is correspondingly reflected, whereby the reflecting system is arranged such that the beam path is deflected at the desired angle needed for the special stereomicroscope, in particular for an ergonomical working of a surgery microscope. In order that work can be done also normally with an inventively constructed stereomicroscope, that is without the funduscopy lenses, and then too an upright, unreversed image is obtained, the additionally inserted double-refracting, reflecting system is exchanged with a 90.degree. prism which again covers both beam paths and has the same optical path length as the double-refracting, reflecting system. This assures that during an exchanging of the reflecting systems, a new focusing of the stereomicroscope is not necessary. Such a capability of exchanging of the systems, which is carried out advantageously in a simple manner by arranging both systems on a common carriage, is necessary because especially during eye surgeries, a suitable reversal of the image is needed, depending on whether work is done in front of or behind the eye lens.